Reduced engine operation times in hybrid vehicles enable fuel economy and reduced regulated emissions benefits. However, the shorter engine operation times combined with low intake manifold vacuum may lead to insufficient purging of fuel vapor from a vapor canister coupled between the intake manifold and the fuel tank. Further, during conditions such as relatively warm ambient temperatures when fuel vapor generation in the fuel tank is increased, insufficient purging of the vapor canister may result in an increase in hydrocarbon emission to the atmosphere.
The inventors herein have recognized the above issue and have devised an approach to at least partly address it. In one example, a method for a fuel system is provided. The method includes, responsive to an operating condition, condensing fuel vapor in a vapor cooler disposed in a fuel tank and routing condensed fuel vapor to a fuel pump.
By condensing the fuel vapor within the fuel tank, a sealed fuel tank may be employed and fuel vapor purging to a vapor canister may be at least partially reduced. Further, fuel tank pressure control may be achieved even when a hybrid vehicle is operating with the engine off. Specifically, by using electronic air conditioning systems, fuel tank pressure can be controlled by vapor condensation in HEVs during engine-off times or before the engine is scheduled to start. The condensate or liquefied vapor that is collected during the engine-off time can then be injected into the fuel pump and or fuel line as soon as the engine is started. Further still, because the condensed fuel vapor is routed directly to the fuel pump and not to the fuel tank, fuel vapor generation in the tank can be reduced and the fuel can be directly supplied to the engine without recycling through the tank and corresponding components.
In a further embodiment, the vapor cooler may be in fluid communication with a cooling system of the vehicle other than the engine's coolant system, for example, via an air conditioner. As such, cooling system controls may be adjusted based on fuel tank parameters. For example, a radiator fan speed may be adjusted based on the temperature of the fuel tank. If the fuel tank temperature is relatively high and a heat transfer to the cooling fluid from the vapor cooler is relatively large, the radiator fan speed may be increased.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.